The invention disclosed herein relates generally to plunger operated switching devices of the type having at least one cantilevered strip carrying a movable contact near its free end, and more particularly to such a device in which contact closure forces are isolated from operator force on the plunger.
A variety of plunger operated switch designs are known in which a movable contact is mounted on a leaf spring. These include three terminal switches having two fixed contacts and a movable contact on a leaf spring which is biased for normal closure with one of the contacts. A plunger operating on the leaf spring may be actuated to press the leaf spring toward the other fixed contacts so as to bring the movable contact into engagement therewith.
Four terminal switch designs are also known utilizing the same principles of operation. In such switch devices, there may be a pair of fixed contacts between which are located a pair of movable contacts, each carried on a leaf spring. The leaf springs may be configured so that the movable contact on one leaf spring is biased for engagement with its adjacent fixed contact and the movable contact on the other leaf spring is biased for separation from its adjacent fixed contact. The leaf springs are maintained at a constant separation and moved relative to the fixed contacts by a plunger which, when actuated, opens the normally closed set of contacts and presses the normally open movable contact into engagement with its adjacent fixed contact.
Such arrangements, and particularly the latter arrangement have certain disadvantages. These stem at least in part from the fact that the switch housing, and consequently the plunger, may not be mounted in a precise or exactly known location relative to the operator which operates the plunger, the plunger may not be precisely located relative to the contacts, and the operator may not always exert the same force on the plunger. Thus, the set of contacts closed by actuation of the plunger may be subject to varying contact forces which could vary the quality of the electrical path.